Method for determining power boosting level of PTRS for removing phase noise in wireless communication system and device therefor

ABSTRACT

According to an embodiment of the present specification, provided is a method for transmitting a signal that allows a user equipment to cancel phase noise by a base station in an mmWave communication system. In this case, the method may include: generating a PTRS for estimating phase noise of a downlink signal; transmitting PTRS power boosting level information for the PTRS to the user equipment via downlink signaling; and transmitting the PTRS via downlink signaling based on the PTRS power boosting level information. In this case, the PTRS power boosting level information may be determined based on at least one of MCS level and PRB size.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/065,122, filed on Jun. 21, 2018, now U.S. Pat. No. 10,461,907, whichis the National Stage filing under 35 U.S.C. 371 of InternationalApplication No. PCT/KR2017/012667, filed on Nov. 9, 2017, which claimsthe benefit of U.S. Provisional Application No. 62/419,473, filed onNov. 9, 2016, 62/444,296, filed on Jan. 9, 2017. 62/501,816, filed onMay 5, 2017, 62/511,944, filed on May 26, 2017 and 62/557,071, filed onSep. 11, 2017, the contents of which are all hereby incorporated byreference herein in their entirety.

TECHNICAL FIELD

The present specification relates to a wireless communication system,and more particularly, to a method for determining power boosting levelof a phase tracking reference signal (PTRS) for phase noise cancellationand apparatus therefor.

BACKGROUND ART

An ultra-high frequency radio communication system using mmWave isconfigured to operate at a center frequency in the range of several GHzto several tens of GHz. Due to such a center frequency feature,significant path loss may occur in a shadow area in the mmWavecommunication system. Considering that a synchronization signal shouldbe stably transmitted to all user equipments (UEs) located withincoverage of a base station (BS), the synchronization signal needs to bedesigned and transmitted in consideration of the potential deep-nullphenomenon, which may occur due to the above-described ultra-highfrequency band characteristic, in the mmWave communication system.

DISCLOSURE OF THE INVENTION Technical Task

The present invention is contrived to solve the aforementioned problems.Accordingly, an object of the present invention is to provide a methodfor determining power booting level of a PTRS.

Another object of the present invention is to achieve accurate decodingof received signals by improving a phase noise cancellation procedureperformed by a user equipment (UE) in a wireless communication system.

A further object of the present invention is to provide a method forimproving efficiency of signal transmission for phase noisecancellation.

Still another object of the present invention is to improvereceiving-side operation by providing information on the signaltransmission for the phase noise cancellation.

Still a further object of the present invention is to provide a methodof transmitting a signal for the phase noise cancellation by consideringcompensation for phase noise and reference signal overhead.

Technical Solution

According to an embodiment of the present specification, provided is amethod for transmitting a signal for phase noise cancellation by a basestation (BS) in an mmWave communication system, including: generating aphase tracking reference signal (PTRS) for estimating phase noise of adownlink signal; transmitting PTRS power boosting level information forthe PTRS to a user equipment (UE); and transmitting the PTRS viadownlink signaling based on the PTRS power boosting level information.In this case, the PTRS power boosting level information may bedetermined based on at least one of the number of PTRS ports, the numberof DMRS ports associated with the PTRS ports, or the number of DMRSports in a DMRS port group associated with the PTRS ports.

According to an embodiment of the present specification, provided is abase station (BS) for transmitting a signal for phase noise cancellationin an mmWave communication system, including: a receiver configured toreceive signals from external devices; a transmitter configured totransmit signals to external devices; and a processor configured tocontrol the receiver and the transmitter. In this case, the processormay be configured to: generate a phase tracking reference signal (PTRS)for estimating phase noise of a downlink signal; transmit PTRS powerboosting level information for the PTRS to a user equipment (UE) viadownlink signaling; and transmit the PTRS based on the PTRS powerboosting level information via downlink signaling. At this time, thePTRS power boosting level information may be determined based on atleast one of the number of PTRS ports, the number of DMRS portsassociated with the PTRS ports, or the number of DMRS ports in a DMRSport group associated with the PTRS ports.

Additionally, the following items can be commonly applied to a methodand apparatus for transmitting a signal for phase noise cancellation inan mmWave communication system.

According to an embodiment of the present specification, the PTRS powerboosting level information may indicate at least one of an on/off stateof PTRS power boosting and a level value of the PTRS power boosting.

Additionally, according to an embodiment of the present specification,the PTRS power boosting level information for the PTRS may betransmitted to the UE explicitly or implicitly.

In this case, according to an embodiment of the present specification,the PTRS power boosting level information may be transmitted to the UEthrough DCI or RRC signaling.

Additionally, according to an embodiment of the present specification,the PTRS power boosting level information may be configured for the UEbased on a predetermined rule.

In this case, according to an embodiment of the present specification,the predetermined rule may mean that the level value of the PTRS powerboosting is determined based on the number of layers.

Additionally, according to an embodiment of the present specification,the predetermined rule may mean that the level value of the PTRS powerboosting is determined based on the number of PTRS ports.

Additionally, according to an embodiment of the present specification,the predetermined rule may mean that the level value of the PTRS powerboosting is determined based on the number of activated PTRS ports.

Additionally, according to an embodiment of the present specification,the level value of the PTRS power boosting may be any one of 3 dB, 4.77dB, 6 dB and 9 dB.

Additionally, according to an embodiment of the present specification,when it is assumed that the number of layers is L, the level value ofthe PTRS power boosting may be determined according to the followingequation: Power boosting level=10×Log 2(L)+Z dB, where Z may beindicated through at least one of RRC and DCI.

Additionally, according to an embodiment of the present specification, Zmay be implicitly determined by MCS level. In this case, if the MCSlevel is equal to or lower than a threshold, Z may be set to 3 dB. Onthe contrary, if the MCS level is higher than the threshold, Z may beset to 0 dB.

Additionally, according to an embodiment of the present specification,the number of DMRS ports may correspond to the number of layers.

Additionally, according to an embodiment of the present specification,the level value of the PTRS power boosting may be expressed as an EPREratio between the PTRS and a physical downlink shared channel (PDSCH).

Advantageous Effects

According to the present specification, received signals can beaccurately decoded by improving a phase noise cancellation procedureperformed by a user equipment (UE) in a wireless communication system.

According to the present specification, a method for improvingefficiency of signal transmission for phase noise cancellation can beprovided.

According to the present specification, receiving-side operation can beimproved by providing information on the signal transmission for thephase noise cancellation.

According to the present specification, a method for determining powerboosting level of a PTRS can be provided.

According to the present specification, a method of transmitting asignal for the phase noise cancellation by considering compensation forphase noise and reference signal overhead can be provided.

It will be appreciated by persons skilled in the art that the effectsthat can be achieved through the present specification are not limitedto what has been particularly described hereinabove and other advantagesof the present invention will be more clearly understood from thefollowing detailed description.

DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating phase distortion due to phase noise.

FIG. 2 is a diagram illustrating block error rate (BLER) performanceaccording to PTRS density in the frequency domain.

FIG. 3 is a diagram illustrating BLER performance according to PTRSdensity in the time domain.

FIG. 4 is a diagram illustrating spectral efficiency for PTRS densityaccording to different TRB size.

FIG. 5 is a diagram illustrating BLER performance according to carrierfrequency offset (CFO).

FIG. 6 is a diagram illustrating BLER performance according to PTRSmapping order: time first mapping and frequency first mapping.

FIG. 7 is a diagram illustrating PTRS allocation patterns.

FIG. 8 is a diagram illustrating BLER performance measured based onPTRSs.

FIG. 9 is a diagram illustrating BLER performance measured based onPTRSs.

FIG. 10 is a diagram illustrating BLER performance measured based onPTRSs.

FIG. 11 is a diagram illustrating BLER performance measured based onPTRSs.

FIG. 12 is a diagram illustrating PTRS arrangement methods.

FIG. 13 is a diagram illustrating different PTRS patterns depending onMCS and PRB.

FIG. 14 is a diagram illustrating the number of PTRSs defined in thefrequency domain depending on PRB size and spectral efficiency inaccordance with presence of PTRS power boosting.

FIG. 15 is a diagram illustrating spectral efficiency at different MCSlevel.

FIG. 16 is a diagram illustrating spectral efficiency at different MCSlevel.

FIG. 17 is a diagram illustrating a method for applying multiplexing toorthogonal PTRS ports.

FIG. 18 is a diagram illustrating PTRS port patterns.

FIG. 19 is a diagram illustrating a method for performing power boostingbased on an activated PTRS port.

FIG. 20 is a diagram illustrating a method for performing power boostingbased on activated PTRS ports.

FIG. 21 is a flowchart illustrating a method for transmitting a signalfor phase noise cancellation by a BS in a communication system.

FIG. 22 is a diagram illustrating a method for determining whether toperform PTRS power boosting.

FIG. 23 is a diagram illustrating the configuration of a user equipmentand a base station according to an embodiment of the present invention.

BEST MODE FOR INVENTION

Although the terms used in the present invention are selected fromgenerally known and used terms, terms used herein may be varieddepending on operator's intention or customs in the art, appearance ofnew technology, or the like. In addition, some of the terms mentioned inthe description of the present invention have been selected by theapplicant at his or her discretion, the detailed meanings of which aredescribed in relevant parts of the description herein. Furthermore, itis required that the present invention is understood, not simply by theactual terms used but by the meanings of each term lying within.

The following embodiments are proposed by combining constituentcomponents and characteristics of the present invention according to apredetermined format. The individual constituent components orcharacteristics should be considered optional factors on the conditionthat there is no additional remark. If required, the individualconstituent components or characteristics may not be combined with othercomponents or characteristics. In addition, some constituent componentsand/or characteristics may be combined to implement the embodiments ofthe present invention. The order of operations to be disclosed in theembodiments of the present invention may be changed. Some components orcharacteristics of any embodiment may also be included in otherembodiments, or may be replaced with those of the other embodiments asnecessary.

In describing the present invention, if it is determined that thedetailed description of a related known function or construction rendersthe scope of the present invention unnecessarily ambiguous, the detaileddescription thereof will be omitted.

In the entire specification, when a certain portion “comprises orincludes” a certain component, this indicates that the other componentsare not excluded and may be further included unless specially describedotherwise. The terms “unit”, “-or/er” and “module” described in thespecification indicate a unit for processing at least one function oroperation, which may be implemented by hardware, software or acombination thereof. The words “a or an”, “one”, “the” and words relatedthereto may be used to include both a singular expression and a pluralexpression unless the context describing the present invention(particularly, the context of the following claims) clearly indicatesotherwise.

In this specification, the embodiments of the present invention havebeen described based on a data transmission and reception relationshipbetween a mobile station and a base station. Here, the base station maymean a terminal node of the network which directly communicates with themobile station. In this document, a specific operation described asperformed by the base station can also be performed by an upper node ofthe base station.

That is, in the network consisting of a plurality of network nodesincluding the base station, various operations performed forcommunication with the mobile station may be performed by the basestation or other network nodes except the base station. The term “basestation” may be replaced with terms such as “fixed station”, “Node B”,“eNode B (eNB)”, “advanced base station (ABS)”, “access point”, etc.

The term “mobile station (MS)” may be replaced with terms such as “userequipment (UE)”, “subscriber station (SS)”, “mobile subscriber station(MSS)”, “mobile terminal”, “advanced mobile station (AMS)”, “terminal”,etc.

In addition, a transmitting end refers to a fixed and/or mobile nodethat transmits data or voice services, and a receiving end refers to afixed and/or mobile node that receive data or voice services.Accordingly, in uplink, the mobile station and base station maycorrespond to the transmitting end and receiving end, respectively.Similarly, in downlink, the mobile station and base station maycorrespond to the receiving end and transmitting end, respectively.

When a device performs communication with a ‘cell’, it may indicate thatthe device transmits and receive signals with a base station of thecell. That is, although the device actually transmits and receivessignals with a specific base station, it can be interpreted to mean thatthe device transmits and receives signals with a cell formed by thespecific base station. Similarly, “macro cell” and/or “small cell” maymean not only specific coverage but also “macro base station supportingthe macro cell” and/or “small cell base station supporting the smallcell”.

The embodiments of the present invention can be supported by standarddocuments disclosed in at least one of wireless access systems includingthe IEEE 802.xx system, 3GPP system, 3GPP LTE system, and 3GPP2 system.That is, the steps or parts, which are not explained to clearly revealthe technical idea of the present invention, in the embodiments of thepresent invention may be supported by the above documents.

In addition, details of all terms mentioned in the present document canbe found in the above standard documents. In particular, the embodimentsof the present invention can be supported by at least one of documentsP802.16e-2004, P802.16e-2005, P802.16.1, P802.16p and P802.16.1b, whichare standard documents for the IEEE 802.16 system.

Hereinafter, the preferred embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings. It isto be understood that the detailed description which will be disclosedalong with the accompanying drawings is intended to describe theexemplary embodiments of the present invention and is not intended todescribe a unique embodiment for carrying out the present invention.

It should be noted that specific terms disclosed in the presentinvention are provided for better understanding of the present inventionand these specific terms may be changed to other terms without departingfrom the technical scope or spirit of the present invention.

1. Phase Noise Analysis and Phase Tracking Reference Signal (PTRS)Design

FIG. 1 is a diagram illustrating phase distortion due to phase noise.The phase noise can be defined as fluctuation in the phase of a signaloccurring during a short time. In this case, since the phase noise couldrandomly change the phase of the received signal in the time domain, itmay interrupt the reception of the signal. For example, referring toFIG. 1(a), the phase noise may randomly occur. However, the phase noisemay show certain correlation between adjacent time samples, which causescommon phase error (CPE) and inter carrier interference (ICI) in thefrequency domain.

FIG. 1(b) shows the effect of CPE and ICI on received constellationpoints. It can be seen from FIG. 1(b) that in square ‘A’, allconstellation points are rotated in three degrees, which results fromCPE. In addition, in circle ‘B’, constellation points are randomlyplaced, which results from ICI. Accordingly, CPE needs to be compensateddue to the phase noise, and to this end, a phase tracking referencesignal (PTRS) may be used for CPE estimation. Table 1 below showssimulation conditions related to the phase noise.

TABLE 1 PN Model PN model 2 in [2] CFO 0 kHz Carrier Frequency 30 GHz #of Traffic RBs 4/64 Subcarrier Spacing 60 kHz # of System RBs 100Channel TDL-B(30 ns, 0 km/h) Modulation 64QAM Channel Estimation IdealCode Rate 5/6 CPE Estimation Real

Referring to Table 1, it can be seen how the PTRS impacts on the CPEestimation if the number of traffic RB is changed.

FIG. 2 is a diagram illustrating block error rate (BLER) performanceaccording to PTRS density in the frequency domain. Specifically, FIGS.2(a) and (b) show the result of measuring the BLER performance when thePTRS density is changed to 0, 1, 4, 8, and 16 in an OFDM symbol in thefrequency domain. In this case, “PTRS=0” indicates no CPE compensation,and “Ideal” indicates the state in which CPE compensation is performed.More specifically, FIG. 2(a) shows the result of measuring the BLERperformance by changing the PTRS density in the frequency domain in thecase of 4-TRB, and FIG. 2(b) shows the result of measuring the BLERperformance by changing the PTRS density in the frequency domain in thecase of 64-TRB.

By comparing FIGS. 2(a) and 2(b), it can be seen that BLER performancedifference according to the PTRS density increases as TRB sizeincreases. Specifically, it can be seen from FIG. 2(a) where the TRBsize is small that BLER performance difference between no CPEcompensation and CPE compensation with PTRS=8 is only 1 dB. However,from FIG. 2(b) where the TRB size is large, it can be seen that BLERperformance difference between no CPE compensation and CPE compensationwith PTRS=8 is 5.8 dB.

In addition, referring to FIG. 2(b), it can be observed that as the PTRSdensity increases, the BLER performance is improved up to the ideal casebased on the CPE compensation. Specifically, referring to FIG. 2(b),when the PTRS density is equal to or higher than 4, ideal BLERperformance can be achieved. Thus, when the PTRS density is 4 or 8, theCPE compensation can be sufficiently achieved. In FIGS. 2(a) and 2(b),when the PTRS density is 4 or 8, the CPE compensation can besufficiently achieved regardless of the TRB size.

FIG. 3 is a diagram illustrating BLER performance according to PTRSdensity in the time domain.

FIG. 3 shows the result of measuring the BLER performance by changing aPTRS interval in the time domain. In FIG. 3, the number of PTRSs in oneOFDM symbol is 4. Referring to FIG. 3, it can be seen that the result issimilar to that of FIG. 2. Specifically, it can be observed that as TRBsize increases, BLER performance difference according to the PTRSdensity in the time domain increases. That is, when the TRB size issmall (4 TRBs in FIG. 3), it is possible to obtain similar BLERperformance without significant effects of the PTRS density in the timedomain. However, it can be seen that when the TRB size is large (64 TRBsin FIG. 3), the BLER performance is significantly changed according tothe PTRS density in the time domain. In other words, the BLERperformance difference according to the PTRS density sensitively changesas the TRB size increases.

FIG. 4 is a diagram illustrating spectral efficiency for PTRS densityaccording to different TRB size.

FIG. 4(a) shows spectral efficiency according to the number of PTRSswhen TRB size is 4. Referring to FIG. 4(a), it can be seen that when theTRB size is 4, no CPE compensation has better spectral efficiency thanCPE compensation with a certain number of PTRSs. When the TRB size is 4,only a single codeblock can be defined in a codeword. In addition, sincethe codeblock spreads out in the subframe, the impact of the phase noisemay be reduced. In this case, similar to FIG. 2(a), when the TRB size issmall, the CPE compensation is not significantly affected. Meanwhile,since information size increases as the number of PTRSs increases,throughput loss may occur due to a region where the PTRSs are allocated.In addition, when the TRB size is small, throughput loss may be greaterthan gain obtained from the CPE compensation, and thus PTRSs may berequired no longer.

Meanwhile, referring to FIG. 4(b), it can be seen that when the TRB sizeis 64, the spectral efficiency is close to the ideal one as the numberof PTRSs increases. This is because since when the TRB size is large, aplurality of codeblocks can be defined in one codeword and eachcodeblock spreads out in one or two OFDM symbols, it may significantlyaffects the phase noise. That is, when high phase noise occurs in aspecific OFDM symbol, it may be difficult to successfully decodecodeblocks located in the specific OFDM symbol. It can be similarlyapplied to FIG. 2(b). In other words, as the TRB size increases, thephase noise impact increases and overhead caused by PTRSs relativelydecreases. Thus, when the number of PTRSs increase, throughput can beimproved.

FIG. 4(c) shows the effect of changes in the PTRS density in the timedomain, and it is similar to FIG. 3. That is, when the TRB size issmall, the PTRS time density may not significantly affect thethroughput. However, as described above, when the TRB size is large, thethroughput may significantly vary according to the PTRS time density.

FIG. 5 is a diagram illustrating BLER performance according to carrierfrequency offset (CFO).

As described above, when the TRB size is small, the PTRS may becomeunnecessary. Nevertheless, the PTRS could be required for even small TRBbecause of CFO caused by oscillator error and Doppler. Referring to FIG.5, it can be seen that in the case of CFO=1.4 kHz, BLER performance isdegraded even when the TRB size is small, for example, 4. In this case,considering that CFO between the BS and UE may be ±0.1 ppm, the maximumCFO may be equal to 3 kHz for 30 GHz. That, when high frequency is used,the CFO may significantly affect the BLER performance. Therefore, thenumber of PTRSs should be determined in consideration of the CPEcompensation and PTRS overhead, which are in a trade-off relationship,and it will be described later.

FIG. 6 is a diagram illustrating BLER performance according to PTRSmapping order: time first mapping and frequency first mapping.

FIG. 6 shows a case where PTRSs are first mapped in the time domain anda case where PTRSs are first mapped in the frequency domain. Referringto FIG. 6, it can be seen that the case where PTRSs are first mapped inthe time domain has better BLER performance than the case where PTRSsare first mapped in the frequency domain. This is because of theaforementioned ICI. That is, since when a codeblock is spread out in thetime domain, the phase noise impact is reduced, the graph shown in FIG.6 can be obtained. In addition, this also implies that codeblockspreading in the time domain is effective for reducing the phase noise,and details will be described later.

2. PTRS Design in Consideration of MCS Level

As described above, the PTRS needs to be used by considering the phasenoise impact. In this case, PTRSs should be allocated by consideringreference signal overhead as described above.

FIG. 7 is a diagram illustrating PTRS allocation patterns. Referring toFIG. 7, patterns #1 has a time period of 1, patterns #2 has a timeperiod of 2, and patterns #4 has a time period of 4. That is, pattern #1is a pattern where PTRSs are allocated with the highest density in thetime domain, and pattern #3 is a pattern where PTRSs are allocated withthe lowest density in the time domain. Table 2 below shows simulationsetup configuration to check how each PTRS pattern shown in FIG. 7affects performance degradation. For example, in Table 2, CFO may berandomly selected from the range of −3 kHz to 3 kHz, and modulation &code rate may be set to QPSK (1/2), 16QAM (3/4) and 64QAM (5/6).

TABLE 2 PN Model PN model 2 in [4] CFO [−3 kHz, 3 kHz] Carrier Frequency30 GHz # of Physical RBs 4/32 Subcarrier 60 kHz # of System RBs 100Spacing Channel CDL-C (30 ns, Modulation & QPSK (1/2), 3 km/h) Code Rate16QAM (3/4), 64QAM (5/6) Channel Ideal CPE Estimation Real Estimation

FIGS. 8 to 11 shows the results of measuring BLER performance based onTable 2, and from the drawings, the PTRS effect can be understood.

In this case, for example, FIG. 8(a) shows the impact of frequencyoffset on BLER performance in the absence of phase noise. Referring toFIG. 8(a), it can be seen that when there is no CFO compensation, theBLER performance is degraded even if an MCS level is low as QPSK (1/2),whereas when the CFO compensation is performed, the BLER performance canbe maintained. That is, the CFO compensation can affect the BLERperformance even at a low MCS level.

In addition, for example, FIG. 8(b) shows the impact of phase noise onBLER performance in the absence of frequency offset. Here, it can beseen that when the MCS level is high as 64QAM (5/6), the BLERperformance is improved through CPE compensation, whereas when the MCSlevel is low as 16QAM (3/4), the same BLER performance is obtainedregardless of whether the CPE compensation is performed. That is, as theMCS level is higher, the impact of the phase noise on the BLERperformance may increase.

FIG. 9 shows elements that impact BLER performance when both phaseoffset and phase noise exist. It can be seen from FIG. 9 that the BLERperformance significantly changes according to different PTRS patterns.That is, when both the frequency offset and phase noise exist, BLERperformance degradation can be determined according to PTRS patterns.

FIG. 10 shows spectral efficiency according to MCS level. Referring toFIGS. 10(a) and 10(b), it can be seen that in the case of QPSK (1/2) and16QAM (3/4), patterns #1, #2 and #3 shown in FIG. 7 achieve highspectral efficiency regardless of PRB size. That is, high spectralefficiency can be achieved because the phase noise impact can benegligible at low MCS level. In this case, for example, in FIG. 10(a),pattern #3 can achieve high spectral efficiency due to small PRB sizeconsidering reference signal overhead as described above.

FIG. 11 shows spectral efficiency according to MCS level. Referring toFIG. 11(a), it can be seen that in the case of 4 PRBs, patterns #1, #2and #3 shown in FIG. 7 achieve high spectral efficiency regardless ofPRB size. That is, high spectral efficiency can be achieved because thephase noise impact can be negligible at low MCS level. In this case, forexample, in FIG. 11(a), pattern #3 can achieve high spectral efficiencydue to small PRB size considering reference signal overhead as describedabove.

Referring to FIG. 11(b), it can be seen that in the case of 64QAM (5/6)and 32 PRBs, patterns #1 and #2 achieve high spectral efficiency. Thisis because since in the case of 32 PRBs, several codeblocks are definedin a codeword, and each codeblock spreads out in one or two OFDMsymbols, it may significantly affects the phase noise. That is, whentransmission is performed based on high MCS level and large PRB size,the phase noise may be affected more as described above.

In this case, for example, each UE can use the PTRS in performing uplinktransmission. However, when there are a plurality of UEs, that is, inthe case of UL MU-MIMO transmission, reference signal overhead mayincrease as the number of UEs increases. Thus, when the MCS level andPRB size are low and small, it should be determined whether the PTRSwill be used, by considering the reference signal overhead.

As another example, in the case of DL transmission, since repeatedlytransmitted signals (e.g., PSS, SSS) or channels (e.g., PBCH) arealready designed, CFO can be estimated in advance of data reception.Thus, a PTRS pattern for high MCS level and large PRB size can beconfigured before data reception, but the invention is not limitedthereto.

In addition, regarding the aforementioned reference signal, which isused in consideration of the phase noise and frequency offset, theconfiguration shown in Table 3 can be applied to design thereof, but theinvention is not limited thereto.

TABLE 3 Agreements:  For CP-OFDM waveform, for the RS enabling phasetracking, the  following should be studied:   Time domain pattern   Alt-1: Continuous mapping, i.e., on every OFDM symbol    Alt-2:Non-continuous mapping, e.g., every other OFDM symbol    Switchingbetween Alt-1 and Alt-2 can also be considered   Frequency domainpattern    Alt-A: Shared and across full carrier bandwidth with fixed   density/spacing    Alt-B: Within each UE's scheduled bandwidth andwith    configurable density/spacing    Other patterns are not precluded  Other properties    UE-specific and/or non-UE-specific    Portmultiplexing such as FDM/TDM/CDM    Potential sharing acrossusers/streams    On-off configuration Agreements:  At least thefollowing RSs are supported for NR downlink   CSI-RS: Reference signalwith main functionalities of CSI   acquisition, beam management    FFS:RRM measurement   DM-RS: Reference signal with main functionalities ofdata and   control demodulation    FFS: channel state informationestimation and interference    estimation    FFS: beam management  Reference signal for phase tracking    FFS: Whether DM-RS extensioncan be applied or not    FFS whether new RS or RS for otherfunctionalities can be used   Reference signal for time/freq. tracking   FFS whether new RS or RS for other functionalities can be used  Reference signal for Radio link monitoring    FFS whether new RS or RSfor other functionalities can be used   RS for RRM measurement    FFSwhether new RS or RS for other functionalities can be used  At least thefollowing RSs are supported for NR uplink   SRS: Reference signal withmain functionalities of CSI acquisition,    beam management    FFS: RRMmeasurement   DM-RS: Reference signal with main functionalities of dataand   control demodulation    FFS: beam management   Reference signalfor phase tracking    FFS: Whether DM-RS extension can be applied or not   FFS whether new RS or RS for other functionalities can be used   FFS:Reference signal for RRM measurement    FFS whether new RS or RS forother functionalities can be used

Proposal 1 (Fixing the Number of PTRSs in the Frequency Domain)

Referring to the drawings, it can be seen that when the number of PTRSsin the frequency domain is 4 or 8, a BLER performance curve approachesthat in the ideal case. That is, the number of PTRSs in the frequencydomain can be determined irrespective of the number of TRBs (or TRBsize). In other words, the number of PTRSs in the frequency domain canbe fixed to a specific value regardless of the number of TRBs.

Specifically, if the number of PTRSs in the frequency domain is assumedto be N, N can be defined as follows

1. N is determined as 4 or 8 regardless of the number of TRBs (N may bedefined as a rule in the specification).

2. The value of N is informed through RRC and/or DCI.

That is, the number of PTRSs in the frequency domain may be determinedas a predetermined specific value, for example, 4 or 8. As anotherexample, the number of PTRSs in the frequency domain can be informedthrough RRC or DCI in advance. In this case, the above-described methodscan be used by considering overhead caused by the PTRS as a referencesignal.

FIG. 12 is a diagram illustrating PTRS arrangement methods. For example,in FIG. 13, the number of PTRSs in the frequency domain may be 4. Inthis case, a distributed type of PTRS and a localized type of PTRS canbe used. For example, the distributed type means to design a frequencyspacing between PTRSs to be uniform within a given TBS. On the otherhand, the localized type means to locate PTRSs at the center of thegiven TBS or a specific position.

In this case, for example, the BS may inform the UE whether thedistributed type or the localized type is used through RRC and/or DCI.Alternatively, one type may be defined as a predetermined arrangementmethod (one of the types may be defined as a rule in the specification).In addition, in the case of uplink transmission, control information maybe signaled together, or a predetermined arrangement method may be used.However, the invention is not limited thereto.

As another example, the number of PTRSs in the frequency domain may bechanged in consideration of TRB size.

This is because ICI caused by CFO degrades CFO and CPE estimationperformance. In this case, as shown in the drawings, as the number ofTRBs increases, the estimation performance is degraded, and thus theBLER performance may be degraded as well. However, since referencesignal overhead decreases as the number of TRBs increases, it ispossible to improve the estimation performance by allocating more PTRSsin the frequency domain. That is, the number of PTRSs in the frequencydomain can be determined based on the number of TRBs by considering theBLER performance degradation and PTRS overhead. For example, the numberof PTRSs can be defined as shown in Table 4. In this case, according toTable 4, when the number of TRBs (or TRB size) is equal to or smallerthan N, the number of PTRSs in the frequency domain may be set to M1. Onthe contrary, when the number of TRBs is greater than N, the number ofPTRSs in the frequency domain may be set to M2. In this case, forinstance, the reference number of TRBs may be 8. In addition, M1 and M2may be 4 or 8, respectively. However, the present invention is notlimited thereto, and other specific values can also be used.

Additionally, for instance, N, M1, and M2 can be configured through RRCand/or DCI. Further, N, M1, and M2 may be determined in advance (valuesthereof may be defined as a rule in the specification).

TABLE 4 If TRB size <= N (e.g. 8)  # of PTRS in the frequency domain =M1 (e.g.4) Else  # of PTRS in the frequency domain = M2 (e.g.8)

Proposal 2 (Changing an Interval Between PTRSs in the Time DomainAccording to TRB Size)

As described above, spectral efficiency can be changed according PTRSintervals in the time domain. Specifically, it can be seen from FIG. 3that when the TRB size is 4, a case where the interval is 2 has betterspectral efficiency than a case where the interval is 1. On the otherhand, it can be seen that when the TRB size is 64, the case where theinterval is 1 has better spectral efficiency than the case where theinterval is 2. That is, as described above, as the TRB size decrease,the impact of reference signal overhead increases because throughputloss caused by the reference signal overhead may be greater than gaincoming from CPE compensation. On the contrary, as the TRB sizedecreases, the spectral efficiency can be improved due to decrease inthe reference signal overhead and increase in the gain from the CPEcompensation.

In this case, for example, the PTRS interval in the time domain can bedefined as shown in Table 5 below. Specifically, when the TRB size isequal to or smaller than N, the PTRS interval in the time domain may beset to M1. On the contrary, when the TRB size is greater than N, thePTRS interval in the time domain may be set to M2. In this case, M1 maybe greater than M2. For instance, M1 and M2 may be set to 2 and 1,respectively, and N may be set to 8.

In other words, when the TRB size is small, the PTRS time interval maybe increased by considering PTRS overhead. In contrast, when the TRBsize is large, the PTRS time interval may be decreased by consideringthe CPE compensation.

Additionally, for instance, N, M1, and M2 can be configured through RRCand/or DCI. Further, N, M1, and M2 may be determined in advance (valuesthereof may be defined as a rule in the specification).

TABLE 5 If TRB size <= N (e.g. 8),  PTRS time interval = M1(e.g. 2) Else PTRS time interval = M2 (e.g. 1)

As another example, a code rate (CR) and modulation order (MO) may befurther considered in determining the PTRS interval in the time domain.That is, the PTRS time interval can be determined by the TRB size, CR,and/or MO.

In FIG. 4(c), the MO and CR may be set to 64QAM and 5/6, respectively.For example, if the MO and/or CR increases, the PTRS time interval maybe decreased from 2 to 1. Table 5 above can be modified by consideringthe MO and CR as shown in Table 6 below.

In addition, for instance, “If CR<=M (e.g. 5/6)” shown in Table 6 may beconfigured based on the MO, but the invention is not limited thereto.That is, even when the MO and/or CR increases, the PTRS time intervalmay be decreased even if the TRB size is small, but the invention is notlimited thereto.

TABLE 6 If TRB size <= N (e.g. 8)  If CR <= M (e.g. 5/6)  PTRS timeinterval = 2  Else  PTRS time interval = 1 Else   PTRS time interval =1.

As another example, the PTRS can be used for CFO estimation. In thiscase, a BS may determine a random PTRS time interval and then signal tothe UE the determined PTRS time interval. Alternatively, when only theCFO estimation is performed, the PTRS time interval may be determined inadvance between a transmitter and a receiver, and only ON/OFF of thePTRS time interval may be signaled through DCI if necessary.

FIG. 14 is a diagram illustrating different PTRS patterns according toMCS level and PRB size as particular embodiments related to PTRSarrangement in the time domain.

Specifically, FIG. 13 shows a case where PTRS patterns are definedaccording to different MCSs and PRBs, and patterns #1 to #3 maycorrespond to conditions 1 to 3 below. Meanwhile, the following mappingmethod may be configured for the UE through RRC, DCI, and/or a rule.

In this case, regarding the following conditions, pattern #1 has theshorted interval, and pattern #3 may have the longest interval. That is,when the MCS level is high and the PRB size is large, the PTRS timeinterval can be shortened. On the other hand, when the PRB size is smalleven though the MCS level is high, the PTRS timer interval may beincreased. In addition, when the MCS level is low and the PRB size issmall, the longest PTRS time interval may be configured. That is, asdescribed above, as both of the PRB size and MCS level increases, thePTRS time interval may decrease. Based on this feature, different TRBpatterns may be configured according to the MCS level and PRB size, andeach pattern can be defined by considering the PTRS overhead.

1. High MCS (e.g. #26)+large PRB (e.g. 32 PRBs): Pattern 1

2. High MCS (e.g. #26)+middle PRB (e.g. 8 PRBs): Pattern 2

Proposal 3 (PTRS Mapping in Accordance with TRB Size)

The PTRS mapping method can be determined according to the TRB size.That is, one of time first mapping and frequency first mapping may beused according to the TRB size. For example, referring to FIG. 5, it canbe seen that when data is mapped based on time first mapping, it is morerobust to phase noise compared to frequency first mapping. That is, itis possible to reduce the phase noise impact.

In addition, for example, since only a single codeblock is defined in acodeword when the TRB size is small as described above, the effects offrequency first mapping and time first mapping are the same.

However, it can be seen that when the TRB size is large, the time-firstmapping or code spreading in the time domain guarantees higherperformance gain. Consequently, the PTRS mapping method should beconsidered when the TRB size is large, and it can be determined as shownin Table 7 below.

That is, when the TRB size is equal to or smaller than N, data can bemapped based on frequency first mapping. On the contrary, when the TRBsize is greater than N, data can be mapped based on time first mapping,time-domain code spreading, or inter-CB interleaving. However, thepresent invention is not limited thereto.

In addition, for example, N may be set to 8. In this case, N may have adifferent value or defined as a predetermined value (it may be definedas a rule in the specification). Moreover, for example, N may bedetermined through DCI and/or RRC, but the invention is not limitedthereto.

In addition, in the case of an ultra-reliable and low latencycommunications (URLLC) service where decoding latency is very important,frequency first mapping can be always applied regardless of N.

Moreover, when the code rate or modulation order is decreased,performance degradation caused by frequency first mapping is alsodecreased. Thus, in this case, N may be determined based on the TRBsize, CR and/or MO. However, the invention is not limited thereto.

TABLE 7  1. In the case of TRB size <= N (e.g., 8), data is mapped basedon frequency first mapping  2. In the case of TRB size > N, time firstmapping, code spreading in the time domain, or new code spreading isperformed on data

Proposal 4 (a Method of Determining Whether PTRS Transmission will bePerformed)

Whether the PTRS will be transmitted can be determined by TRB size, BScapability, and/or UE capability.

FIG. 4(a) shows that a case in which no PTRS is transmitted has betterspectral efficiency than a case in which the PTRS is transmitted.

Meanwhile, FIG. 5 shows that when CFO of 1.4 kHz occurs, communicationfails if no PTRS is transmitted. In this case, the magnitude of the CFOmay be changed according to oscillators, that is, the UE and BScapabilities. If the CFO magnitude is extremely small due to excellentoscillators of the UE and BS and when the TRB size is small, it isbetter not to transmit the PTRS for high spectral efficiency.

In other words, whether the PTRS will be transmitted can be determinedby the BS capability and UE capability as well as the TRB size. To thisend, the UE may transmit information related to its CFO (e.g.,oscillator, movement, or speed) to the BS. Thereafter, the BS maydetermine whether the PTRS will be transmitted based on the informationreceived from the UE and its capability information. However, theinvention is not limited thereto.

Hereinabove, the PTRS density in the frequency and time domains has beendescribed. In the following description, PTRS arrangement methods willbe explained.

Proposal 5-1 (a Method for Determining PTRS Power Boosting Level)

The PTRS power boosting level can be determined according to MCS leveland/or PRB size (or TRB size). In this case, the PTRS power boostinglevel may be configured for the UE through RRC, DCI, and/or a rule.

Specifically, FIGS. 14 to 16 show spectral efficiency in accordance withthe number of PTRSs defined in the frequency domain and presence of PTRSpower boosting when the PRB size is 4. In this case, the PTRS powerboosting may be defined as ON/OFF states.

For example, FIG. 14 is a diagram illustrating spectral efficiency inthe case of 2 and 4 PTRSs in the state in which the PTRS power boostingis ON/OFF. When an SNR is low, a case where the two PTRSs are used inthe state that the PTRS power boosting is OFF shows poor performancecompared to a case where 4 PTRSs are used. In this case, the noiseimpact may increase at a low SNR. That is, since the noise impactincreases at a low SNR, it is difficult to obtain sufficient CPE and CFOestimation. Thus, the case where the four PTRSs are used shows betterperformance than the case where the two PTRSs are used. Therefore, whenthe SNR is low, it is required to improve the performance by increasingthe number of samples, that is, by referring to the case where the fourPTRSs are used.

On the other hand, when the SNR is high, the noise impact may decrease.Thus, even though the number of PTRSs is small, it is possible to obtainsufficient CPE and CFO estimation. Referring to FIG. 15, when the SNR ishigh, a case where the number of PTRSs is two shows better performancethan a case where four PTRSs are used. That is, in this case, CPE andCFO can be sufficiently measured although the number of PTRSs is small.Since overhead increases as the number of PTRSs increases as describedabove, its performance may be degraded.

As described above, when the PRB size is small and the SNR is low (i.e.,low MCS), the spectral efficiency can be improved by increasing thenumber of PTRSs in the frequency domain. On the other hand, in thiscase, reference signal overhead may increase, and considering MU UL(multiuser uplink), other UEs need to be indicated that the number ofPTRSs in the frequency domain increase, whereby an additional procedureis needed.

In this case, for example, referring to FIG. 14, when the PTRS powerboosting is in the ON state, the case where the two PTRSs are used mayalways have better spectral efficiency than the case where the four PTRSare used. That is, the spectral efficiency can be further improved byturning on the PTRS power boosting compared to increasing the number ofPTRSs in the frequency domain. That is, when the PTRS power boosting ison, the CPE and CFO measurement can be sufficiently performed and thenumber of PTRS samples does not increase so that reference signaloverhead does not also increase. In addition, for example, since thenumber of PTRSs in the frequency domain does not increase in theabove-described situation, it is not necessary to inform other UEs ofincrease or decrease in the number of PTRSs even in the case of MU UL.

In other words, it is possible to improve the performance through thePTRS power boosting by considering the SNR level without increase in thenumber of PTRSs in the frequency domain. In this case, unnecessaryprocedures may also be omitted.

In addition, for example, when the SNR is high, a high MCE can beselected in general. That is, when the SNR is high, a high MCE level maybe selected. On the contrary, when the SNR is low, a low MCS level maybe selected. Thus, a case where the SNR is high may correspond to a casewhere the MCS level is high, and a case where the SNR is low maycorrespond to a case where the MCS level is low. That is, as describedabove, the performance can be improved through the PTRS power boostinginstead of adjusting the number of PTRSs in the frequency domain inaccordance with the MCS level.

Specifically, FIGS. 15 and 16 are diagrams illustrating spectralefficiency at different MCS level. In this case, by comparing a casewhere two PTRSs are used and a case where four PTRSs are used in thestate that boosting is off, it can be seen that the case where the twoPTRSs are used has low spectral efficiency at a low SNR. It is the sameas described above.

In this case, the UE may determine ON/OFF of PTRS power boostingaccording to allocated PRB size and MCS level under consideration of theabove-mentioned situation. For example, the UE may determine ON/OFF ofthe PTRS power boosting either implicitly or explicitly.

In addition, for example, whether the PTRS power boosting is on or offmay be determined as shown in Table 8 below. In this case, if the PRBsize is 4 and the MCS level is equal to or lower than 16QAM, the PTRSpower boosting can be on by setting two PTRSs in the frequency domain.On the other hand, if the PRB size is 4 and the MCS level is higher than16QAM, the PTRS power boosting may be off by setting two PTRSs in thefrequency domain

Moreover, when the PTB size is 32 and the MCS level is equal to or lowerthan 16QAM, the PTRS power boosting may be on by setting four PTRSs inthe frequency domain. Further, when the PRB size is 32 and the MCS levelis higher than 16QAM, the PTRS power boosting may be off by setting fourPTRSs in the frequency domain.

That is, whether the PTRS power boosting is on or off and the number ofPTRSs may be determined according to at least one of the PRB size andMCS level.

In detail, when the PRB size is small and the MCS level is low, theperformance can be improved through the PTRS power boosting bydecreasing the number of PTRSs in the frequency domain. On the otherhand, when the MCS level is high although the PRB size is small, thePTRS power boosting may be off because CPE and CFO can be sufficientlyestimated. In this case, as described above, a high MCE level may beselected at a high SNR in general. In other words, the MCS level maycorrespond to the SNR level.

In addition, referring to the drawings, it can be seen that when the SNRis high, similar performance is obtained regardless of whether the PTRSpower boosting is performed. Therefore, when the MCS level is high, thePTRS power boosting may be off.

In addition, when the PRB size is much larger, if the MCS level is low,the PTRS power boosting may be on without increase in the number ofPTRSs in the frequency domain. Moreover, when the MCS level is high, thePTRS power boosting may be off as described above.

The PRB size and MCS level shown in Table 8 are merely examples. Inaddition, each of them may be configured based on other referencevalues, but the invention is not limited thereto.

TABLE 8 1. PRB size = 4, MCS level<=16QAM(code rate = 3/4)  → The numberof PTRSs in the frequency domain = 2, PTRS  boosting on 2. PRB size = 4,MCS level>16QAM(3/4)  → The number of PTRSs in the frequency domain = 2,PTRS  boosting off 3. PRB size = 32, MCS level<=16QAM(3/4) □  → Thenumber of PTRSs in the frequency domain = 4, PTRS  boosting on 4. PRBsize = 32, MCS level>16QAM(3/4)  → The number of PTRSs in the frequencydomain = 4, PTRS  boosting off

Additionally, for instance, when the PTRS power boosting is on, a powerboosting level value of the PTRS power boosting may be determined. Inthis case, the boosting level value may mean boosting level for averagepower of data symbols. Alternatively, the boosting level value can beexpressed as a PTRS-to-PDCH EPRE ratio. In this case, a PDSCH mayindicate average power of PDSCHs per layer or average power of datasymbols per layer. However, the invention is not limited thereto.

Additionally, for example, the power boosting level may be set to 3/6dB. This value may be configured for the UE through RRC, DCI, and/or arule. However, the invention is not limited thereto.

That is, whether the above-described power boosting is on or off and thePTRS power boosting level value may be configured through RRC, DCI,and/or a rule. In this case, for example, it is possible to indicatewhether the PTRS power boosting is on or off and the PTRS power boostinglevel value in different ways. That is, by considering overhead andlatency, whether the PTRS power boosting is on or off is configuredbased on certain conditions, and the PTRS power booting level value maybe signaled. This may be changed according to systems.

As another example, different PTRS power boosting level values may beconfigured according to the number of layers. In this case, for example,in the case of 2/4-layer transmission, power of each layer where eachPDSCH is transmitted may be decreased by 3/6 dB compared to 1-layertransmission. In this case, power of the PTRS may also be decreased by3/6 dB. Thus, to compensate the power reduction, the PTRS power needs tobe boosted by 3/6 dB. However, since unnecessary power boosting is notefficient, the PTRS power boosting value may be set to 3 dB when thenumber of layers is small. That is, the PTRS power boosting level valuemay be determined in consideration of the number of layers, but theinvention is not limited thereto.

In addition, it can be seen from FIG. 16 that when the MCS level is low,3 dB boosting is useful for improving the performance. Thus, consideringthe above-described situation, 3 dB boosting may be necessary for asingle layer, and in the case of 4 layers, 9 dB boosting may be requireddue to power compensation. In this case, for instance, the powerboosting level value can be determined according to Equation 3 inconsideration of the above-described situation. In this case, it can beseen from Equation 1 that the power boosting level value becomes greateras the number of layers increase. Moreover, for example, in Equation 1,the value of Z can be configured through RRC or as a rule (e.g., 3 dB, 6dB, etc.) in the specification. However, the invention is not limitedthereto.

Further, for instance, the value of Z can be implicitly determined. Inthis case, if the MCS level is low, the value of Z may be set to 3 dB.In addition, if the MCS level is high, the value of Z may be set to 0dB. That is, similar to the operation principle, where the powerboosting is on at low MCS level and off at high MCS level, the MCS levelmay be considered in determining the power boosting level. When the MCSlevel is low, higher power boosting level needs to be configured so thatZ can be set to 3 dB. In addition, when the MCS level is high, highpower boosting level is not required so that Z can be set to 0 dB.However, the invention is not limited thereto. Moreover, the MCS levelmay be determined based on a threshold. That is, when the MCS level isequal to or lower than the threshold, Z may be set to 3 dB. On thecontrary, when the MCS level is higher than the threshold, Z may be setto 0 dB. In this case, the threshold may be merely a reference value,and thus it may be configured differently. Further, the invention is notlimited thereto.Power boosting level=10×Log 2(# of layers)+Z dB  [Equation 1]

Additionally, for example, in the above-described configuration, rulesare previously defined between a transmitter and receiver. That is, thismay mean when specific MCS level and PRB size is determined, the UEoperates according to rules without any separate configuration. Forinstance, in the case of PRB size=4 and MCS level<=16QAM (coderate=3/4), the UE may perform PTRS transmission according to thecondition of the number of PTRSs in the frequency domain=2 and 3/6 dB ofPTRS boosting on. That is, the UE may operate according to the PRB sizeand MCS level, which corresponds to one condition.

As another example, the PTRS power boosting can be always performedregardless of the PRB size and MCS level. In this case, for instance,the above-mentioned boosting level value may be configured for the UEthrough RRC, DCI, and a rule. However, the invention is not limitedthereto. That is, since the PTRS power boosting can be always on, it maynot be separately signaled, and only the power boosting level value maybe indicated. However, the invention is not limited thereto.

As described above, the PTRS can be used for noise reduction. In thiscase, whether PTRS power is boosted can be determined according to theaforementioned SNR level (or MCS level). In other words, ON/OFF of thePTRS power boosting can be determined according to the SNR level (or MCSlevel). That is, when the number of PTRS increases, reference signaloverhead increase, and it may cause performance degradation. However, itis possible to improve the performance through the PTRS power boostingwithout increase in the number of PTRSs. Moreover, by doing so, theoverhead may also be reduced because the number of PTRSs in thefrequency domain does not increase. Further, since it is not necessaryto inform other UEs of increase in the number of PTRSs even in the caseof MU UL, efficiency can be improved as well.

Proposal 5-2 (Power Boosting According to PTRS Port Number)

For PTRS ports, orthogonal PTRS multiplexing can be performed. AlthoughFIG. 17 shows orthogonal PTRS multiplexing in downlink, it can beequally applied to uplink. In addition, although the invention isdescribed on the assumption that an orthogonal cover code (OCC) (orcyclic shift (CS)) has a length of 2, the invention is not limitedthereto, that is, can be applied when the OCC has a random length.

For example, when A and B are orthogonal to each other, it may mean thatA and B should use different time/frequency/code resources. On thecontrary, when A and B are non-orthogonal to each other, it may meanthat A and B can use the same time/frequency/code resource. In addition,in FIG. 17, rate matching may mean that the UE does not expect datatransmission in a corresponding region. That is, it may mean that the UEdoes not receive any data in the corresponding region. However, theinvention is not limited thereto.

In addition, PTRS power boosting can be supported by PTRS ports, and FDMcan be applied to the PTRS ports. Moreover, PTRS power boosting levelmay be configured for the UE based on at least one of RRC, MAC-CE, andDCI, or it may be defined as a rule in the specification. This will bedescribed later.

Referring to FIG. 17, for example, four DMR ports and two PTRS ports maybe configured. However, it is able to change the number of DMRs portsand the number of PTRS ports, but the invention is not limited thereto.

For example, two DMRs ports (e.g., DMRS ports #1 and #2) can be definedusing the CS in the frequency domain. In this case, they may be arrangedaccording to comb type 2. Using a liner combination of DMRS ports #1 and#2, (A) and (C) can be defined. That is, it is possible to define [DMRSport #1+DMRS port #2](=(A)) and [DMRS port #1−DMRS port #2](=(C)). Inthis case, based on DMRS ports #1 and #2, PTRS port #1 can be defined as(a) and (c). That is, PTRS port #1 can be defined on the same axis asthe frequency domain in which DMRS ports #1 and #2 are defined.

In addition, for example, (B) and (D) can be defined using a linercombination of DMRS ports #3 and #4. That is, it is possible to define[DMRS port #3+DMRS port #4](=(B)) and [DMRS port #1−DMRS port #2](=(D)).In this case, based on DMRS ports #3 and #4, PTRS port #2 can be definedas (b) and (d). That is, PTRS port #2 can be defined on the same axis asthe frequency domain in which DMRS ports #3 and #4 are defined.

Moreover, for example, in FIG. 17, PTRS port #1 may correspond to either(a) or (c). Similarly, PTRS port #2 may correspond to either (b) or (d).Specifically, a PTRS port may be set to have the same frequency locationin each RB. That is, PTRS port #1 may correspond to either (a) or (c),or it may not be configured. Similarly, PTRS port #2 may correspond toeither (b) or (d), or it may not be configured. For instance, when thetwo PTRS ports are allocated to one UE, PTRS port #1 may be allocated toeither (a) or (c), and PTRS port #2 may be allocated to either (b) or(d). FIG. 17 is an embodiment for showing each case, and it can beindividually interpreted with respect to each RB as described above. Thefrequency-domain position of the PTRS port may be allocated to aposition where at least one DMRS port in a DMRS port group associatedwith the PTRS port is located. In this case, the DMRS port groupassociated with the PTRS port may have the same phase source. Further, atime-domain position of the PTRS port may be determined according topattern #1 or #2 shown in FIG. 18. That is, it may be allocated to allOFDM symbols or based on a certain pattern. However, the invention isnot limited thereto. For instance, the time-domain pattern may beconfigured for the UE through at least one of RRC, MAC CE, and DCI. Inaddition, for example, it may be defined as a rule in the specification.Moreover, multiplexing may be performed on PTRS ports based on SU(single user). Alternatively, multiplexing may be performed on PTRSports based on MU (multi user).

When the PTRS port multiplexing is performed based on the SU, aplurality of PTRS ports may be defined for a single UE in an orthogonalmanner. For example, DMRS ports #1 and #3 may be defined for the UE. Inthis case, a PTRS port corresponding to DMRS port #3 may be PTRS port#3. In this case, PTRS ports may be defined to be orthogonal to eachother.

However, the aforementioned port number may be merely an example.Specifically, a plurality of PTRS ports allocated to one UE may bedefined to be orthogonal, but the invention is not limited to portnumbers. For example, in FIG. 17, PTRS ports #1 and #2 may be allocatedto one UE, and they may be defined to be orthogonal. Although PTRS ports#2 and #3 are mentioned in the present invention, orthogonal PTRS portscan be defined for one UE without being limited to port numbers.

In addition, when the PTRS port multiplexing is performed based on theMU, a plurality of PTRS ports associated with a plurality of DMRS portsdefined using different OCCs (or CSs) may be orthogonal to each other inorder to support the multiplexing.

In this case, for example, the BS may inform the UE of the PTRS powerboosting level using at least one of RRC, MAC-CE, and DCI as describedabove. In addition, the PTRS power boosting level may be defined as arule in the specification.

In this case, for example, when one PTRS port is received in theSU-based case and MU-based case, data may not be transmitted throughanother PTRS port. For instance, when PTRS port #1 is received, data maynot be transmitted through PTRS port #2. In addition, when PTRS port #1is received, data may not be transmitted through PTRS port #3. Thus,power for PTRS port #1 may be boosted using power allocated for PTRSport #2 (or PTRS port #3). In this case, power boosting level may bedefined through association with the number of zero power (ZP) PTRSsdefined in the same OFDM symbol. That is, the power boosting level maybe determined based on the number of PTRS ports of which power is zeroin the same OFDM symbol. In this case, for example, referring to FIG.17, when only one PTRS port is used after configuration of two PTRSports, the power boosting level may be defined as 3 dB.

For instance, the PTRS power boosting level may be expressed as aPTRS-to-PDSCH power ratio. In this case, since if the number of PTRSports is one, there is no ZP PTRS for the power boosting, the PTRS powerboosting level may be set to 0 dB. On the other hand, when there are twoor more PTRS ports, if one PTRS port is received and data is nottransmitted through other ports, the PTRS power boosting level may beset to 3 dB.

Further, the power boosting level can be equally applied to both theSU-based case and MU-based case, but the invention is not limitedthereto.

Proposal 6-1 (Power Boosting in Accordance with PTRS and DMRS Mapping)

Orthogonal multiplexing can be applied to PTRS and data transmission andreception at a single UE. Thus, PTRS resource elements do not overlapwith data resource elements in the UE. In addition, for example, aplurality of PTRSs can be defined for the UE. In this case, assumingthat the number of DMRS ports mapped to an n^(th) PTRS port is Nn andthe total number of DMRS ports is N, the n^(th) PTRS port can bepower-boosted by N/Nn. That is, PTRS power can be boosted by N/Nn inorder to use the maximum available transmit power per resource element.

In this case, for example, the UE may implicitly determine boostinglevel in accordance with a mapping relationship between an n^(th) PTRSand DMRSs. In addition, for example, the possibility of theaforementioned power boosting and/or a boosting value can be explicitlyindicated through at least one of RRC, DCI, and MAC-CE. As anotherexample, the possibility of the aforementioned power boosting and/or theboosting value may be determined by a rule, but the invention is notlimited thereto. Moreover, for example, whether the power boosting isperformed may be configured by the BS through at least one of RRC andDCI, or it may be determined by a rule. However, the invention is notlimited thereto.

As a further example, a mapping relationship between PTRSs and DMRSs maybe implicitly determined by a rule. In addition, for example, themapping relationship between PTRSs and DMRSs may be explicitly indicatedthrough at least one of RRC, DCI, and MAC-CE.

As still another example, when the UE explicitly informs the UE of PTRSports through at least one of RRC, DCI, and MAC-CE, the UE can be awareof the mapping relationship between PTRSs and DMRSs using it.

For instance, PTRS port #1 may be mapped to DMRS ports #1 and #2, andPTRS port #2 may be mapped to DMRS ports #3 and #4. Alternatively, inthis embodiment, PTRS port #1 may be mapped to DMRS port #1, and PTRSport #2 may be mapped to DMRS port #3. However, this is merely anexample, and the invention is not limited to the above-describedembodiment.

Further, the above-described proposal is not limited to uplink but canbe equally applied to downlink for power boosting. However, theinvention is not limited thereto.

Proposal 6-2 (PTRS Power Boosting Based on the Number of Layers inAssociated DMRS Port Group)

PTRS and DMRS ports may be in a quasi-co-location (QCL) relationship.That is, for large scale property, PTRS and DMRS ports may be equallyapplied. However, for example, when PTRS power boosting is performed,QCL may not be applied regarding an average gain between PTRS and DMRSports. That is, in this situation, a separate definition may be requiredfor QCL.

For example, the UE may determine downlink PTRS power boosting levelbased on total layers of a DMRS port group including a PTRS.Specifically, the power boosting level may correspond to a power offsetvalue of a single layer transmitted through a PDSCH. In this case, thelayer may be restricted such that it should be included in the DMRS portgroup associated with the PTRS. In this case, the PTRS power boostinglevel can be determined according to Equation 2 below.PTRS Power boosting level=10×log 10(L)  [Equation 2]

In Equation 2, L is the number of total layers in the DMRS port groupassociated with the PTRS port. That is, the PTRS power boosting levelmay be determined based on the number of total layers in the DMRS portgroup.

For example, it is assumed that two DMRS port groups, i.e., DMRS portgroup #0 and DMRS port group #1 have two and three layers, respectively.In this case, if only DMRS port group #0 transmits PTRS port #0, thePTRS power boosting level becomes 3 dB. That is, in Equation 2, L is 2,and the PTRS power boosting level may be 3 dB>

In addition, for example, the number of layers may correspond to thenumber of DMRS ports. That is, the number of total layers in the DMRSport group may be equal to the number of DMRS ports. In this case, forexample, considering a relationship with Proposal 6-1, Proposal 6-2 maybe applied when a plurality of DMRS port groups exist. For example, DMRSport group #1 and DMRS port group #2 may exist. In this case, it can beassumed that DMRs ports #1 and #2 belong to DMRS port group #1, and DMRSports #3, #4, and #5 belong to DMRS port group #2. If PTRS port #1 andPTRS port #2 correspond to DMRS port #1 and DMRS port #3, respectively,the number of layers may correspond to the number of DMRS ports asdescribed above, and thus PTRS port #1 can be boosted by 10*log 10(2).And, PTRS port #2 can be boosted by 10*log 10(3).

Moreover, for instance, when only DMRS port group #1 transmits PTRS port#0, the PTRS power boosting level may be 4.77 dB. That is, in Equation2, L is 3 and the PTRS power boosting level may be 4.77 dB.

As another example, the UE may determine the PTRS power boosting levelbased on the number of total layers in a DMRS port group including aPTRS and the number of other DMRS port groups where the PTRS istransmitted. Specifically, referring to FIG. 19, it can be seen thatDMRS ports #0 and #1 belong to different DMRS port groups, and only PTRSport #0 is transmitted. In this case, since there is no layer or RE fromwhich power is brought, PTRS port #0 may not be power-boosted. That is,since the number of total layers in the DMRS port group is 1, the powerboosting cannot be performed.

As a further example, data may not be transmitted in a PTRS regionallocated to a different UE. That is, REs for the PTRS may not be usedregardless of whether the different UE uses the PTRS. In this case,since data is not transmitted through PTRS ports, a UE may usecorresponding power for the PTRS power boosting. For instance, when datais not transmitted through port #2, the UE may boost PTRS power for port#1 based on power for port #2. However, the invention is not limitedthereto. In this case, whether the power booting will be performed maybe configured by the BS through at least one of DCI and RRC. Inaddition, it may also be defined in the specification. However, theinvention is not limited thereto.

For example, considering the above-described situation, it is assumedwith reference to FIG. 20 that DMRS ports #0 and #1 belong to differentDMRS port groups, and PTRS ports #0 and #1 are transmitted. In thiscase, there may be another RE from which capable of providing power forPTRS port #0. That is, since there is an RE where PTRS port #1 istransmitted, the PTRS power boosting can be performed.

In other words, if there is an activated PTRS port, the power boostingcan be achieved through an RE for the PTRS port. Thus, Equation 2 can bemodified to Equation 3.PTRS Power boosting level=10×log 10(L)+10×log 10(P)  [Equation 3]

In Equation 3, L is the number of total layers in the DMRS port groupassociated with the PTRS port as described above, and P is the totalnumber of activated PTRS ports. That is, the PTRS power boosting levelcan be determined by considering both the number of total layers in theDMRS port group and the number of activated PTRS ports.

In this case, for example, if the PTRS power boosting level is equal toor greater than a threshold, the PTRS power boosting level may belimited to a specific value. That is, the PTRS power boosting level maybe limited not to exceed the threshold. For example, when the PTRS powerboosting level is equal to or greater than 6 dB, it may be set to 6 dB.In other words, the threshold may be set to 6 dB. In this case, thethreshold may be specified either through a higher layer signal or by arule. Alternatively, it may be defined in the specification in advance.

As a particular example, a case where both DMRS port group #0 and DMRSport group #1 transmit PTRS ports #0 and #1 may be considered. In thiscase, PTRS power boosting level of PTRS port #0 may be limited to 6 dB,and PTRS power boosting level of PTRS port #1 may be limited to 7.77 dB.However, the invention is not limited thereto.

As another example, it is assumed that the number of layers of DMRS portgroup #0 is 2, the number of layers of DMRS port group #1 is 3, thenumber of layers of DMRS port group #2 is 1, and the number of layers ofDMRS port group #3 is 2. In this case, if all the above DMRS port groupstransmit PTRS ports #0, #1, #2, and #3, power boosting level for eachPTRS port may be determined as shown in Table 3. That is, the powerboosting level may be determined based on Equation 3 above.

TABLE 9 PTRS Power boosting level of PTRS port #0 = 10log10(2) +10log10(4) PTRS Power boosting level of PTRS port #1 = 10log10(3) +10log10(4) PTRS Power boosting level of PTRS port #2 = 10log10(1) +10log10(4) PTRS Power boosting level of PTRS port #3 = 10log10(2) +10log10(4)

FIG. 21 is a flowchart illustrating a method for transmitting a signalfor phase noise cancellation by a BS in a communication system.

The BS can generate a PTRS [S2110]. In this case, the PTRS transmittedby the BS may be a reference signal for phase noise cancellation asdescribed above with reference to FIGS. 1 to 20.

Next, the BS can transmit, to a UE, PTRS power boosting levelinformation through downlink signaling [S2120]. In this case, the PTRSpower booting level information may be determined at least one of MCSlevel and PRB size as described above with reference to FIGS. 1 to 20.In addition, for example, the PTRS power boosting level information maybe configured for the UE through RRC, DCI, and/or a rule. In this case,for instance, the PTRS power boosting level information may beinformation indicating ON/OFF of PTRS power boosting. For example, asdescribed above, when the MCS level is lower than a predetermined value,the PTRS power boosting may be on. In this case, for instance, thepredetermined value for the MCS level may be 16QAM. Moreover, when thePRB size is small, the number of PTRSs in the frequency domaindecreases, and the PTRSs may be power-boosted as described above.

That is, when the MCS level is equal to or lower than the predeterminedvalue, the number of PTRSs in the frequency domain may be determined asa preconfigured value by considering the PRB size. In addition, when theMCS level is higher than the predetermined value, the PTRS powerboosting may be off as described above. Moreover, for example, since theMCS level is determined to be higher when an SNR is high, the PTRS powerboosting may be off at the high SNR as described above.

Thereafter, the PTRS can be transmitted based on the PTRS power boostinglevel information [S2130]. In this case, PTRS power boosting level maybe information indicating whether the PTRS power boosting is on or off.In addition, it may be a level value for the PTRS power boosting. Inthis case, for example, the level value for the PTRS power boosting maybe 3 or 6 dB. As another example, the level value for the PTRS powerboosting may be determined based on the number of layers as describedabove.

FIG. 22 is a diagram illustrating a method for determining whether toperform PTRS power boosting. First, PRB size and MCS level can bedetermined [S2210]. In this case, as described above with reference toFIGS. 1 to 21, PTRS power boosting level for PTRSs may be determinedbased on the determined PRB size and MCS level. In this case, as the PRBsize decreases, the number of PTRSs may decrease. In addition, as thePRB size increases, the number of PTRSs may increase. Moreover, forexample, as described above, when an SNR is high, the MCS level may alsobe high in general. Thus, the PTRS power boosting level may bedetermined based on SNR level as described above.

Next, when the MCS level is equal to or lower than a predetermined value[S2220], the number of PTRSs in the frequency domain can be determinedbased on the PRB size, and the PTRS power boosting can be on [S2230]. Onthe other hand, when the MCS level is higher than the predeterminedvalue [S2220], the number of PTRSs in the frequency domain can bedetermined based on the PRB size, and the PTRS power boosting can be on[S2240]. In this case, as described above with reference to FIGS. 1 to21, when the MCS level is equal to or lower than the predeterminedvalue, the PTRS may be transmitted through the PTRS power boostingwithout increase in the number of PTRSs in the frequency domain. Bydoing so, the number of PTRSs does not increase, and thus it is possibleto reduce performance degradation caused by reference signal overhead.Meanwhile, since CPE and CFO estimation performance can also be improvedthrough the PTRS power boosting, the performance degradation can befurther reduced. In addition, for example, the predetermined MCS levelvalue may be 16QAM. However, this is merely an example, and theinvention is not limited to the above-described embodiment.

Moreover, when the MCS level is higher than the predetermined value, thePTRS power boosting can be off without increase in the number of PTRSsin the frequency domain. As described above, high MCS level maycorrespond to a high SNR. In this case, since a certain degree of CPEand CFO estimation performance can be guaranteed due to the high SNR, itis not necessary to perform the PTRS power boosting for the PTRSs.

As another example, when the PTRS power boosting is on, different PTRSpower boosting level values can be configured. In addition, for example,the PTRS power boosting level value may be determined based on thenumber of layers as described above.

As a further example, the PTRS power boosting may be always onregardless of the MCS level. In this case, as still another example, itis able to configure different level values for the PTRS power boostingas described above.

Further, although the invention has been described based on downlinktransmission performed by the BS with reference to FIGS. 1 to 21, it canbe equally applied to uplink transmission. That is, the aforementionedembodiment can be equally applied when a UE generates a PTRS, transmitsPTRS power boosting level information for the PTRS to the BS, and thentransmits the PTRS to the BS.

Device Configuration

FIG. 23 is a diagram illustrating the configuration of a user equipmentand a base station according to an embodiment of the present invention.In FIG. 23, the user equipment 100 and the base station 200 may includeradio frequency (RF) units 110 and 210, processors 120 and 220 andmemories 130 and 230, respectively. Although FIG. 23 shows a 1:1communication environment between the user equipment 100 and basestation 200, a communication environment may be established between aplurality of user equipments and a base station. In addition, theconfiguration of the base station 200 shown in FIG. 23 can be applied toa macro cell base station and a small cell base station.

The RF units 110 and 210 may include transmitters 112 and 212 andreceivers 114 and 214, respectively. The transmitter 112 and thereceiver 114 of the user equipment 100 are configured to transmit andreceive signals to and from the base station 200 and other userequipments, and the processor 120 is functionally connected to thetransmitter 112 and the receiver 114 to control processes performed atthe transmitter 112 and the receiver 114 for transmitting and receivingsignals to and from other devices. The processor 120 processes a signalto be transmitted, sends the processed signal to the transmitter 112,and processes a signal received by the receiver 114.

If necessary, the processor 120 may store information included in anexchanged message in the memory 130. Due to this structure, the userequipment 100 can perform the methods described in various embodimentsof the present invention.

The transmitter 212 and the receiver 214 of the base station 200 areconfigured to transmit and receive signals to and from another basestation and user equipments, and the processor 220 is functionallyconnected to the transmitter 212 and the receiver 214 to controlprocesses performed at the transmitter 212 and the receiver 214 fortransmitting and receiving signals to and from other devices. Theprocessor 220 processes a signal to be transmitted, sends the processedsignal to the transmitter 212, and processes a signal received by thereceiver 214. If necessary, the processor 220 may store informationincluded in an exchanged message in the memory 230. Due to thisstructure, the base station 200 can perform the methods described invarious embodiments of the present invention.

The processors 120 and 220 of the user equipment 100 and the basestation 200 instruct (for example, control, adjust, or manage) operationof the user equipment 100 and the base station 200, respectively. Theprocessors 120 and 220 may be connected to the memories 130 and 230 forstoring program code and data, respectively. The memories 130 and 230are respectively connected to the processors 120 and 220 so as to storeoperating systems, applications and general files.

Each of the processors 120 and 220 of the present invention may becalled a controller, a microcontroller, a microprocessor, amicrocomputer, etc. Each of the processors 120 and 220 may beimplemented by hardware, firmware, software, or any combination thereof.

When the embodiments of the present invention are implemented byhardware, application specific integrated circuits (ASICs), digitalsignal processors (DSPs), digital signal processing devices (DSPDs),programmable logic devices (PLDs), field programmable gate arrays(FPGAs), and the like may be included in the processors 120 and 220.

In case of the implementation by firmware or software, a methodaccording to each embodiment of the present invention can be implementedby modules, procedures, and/or functions for performing theabove-explained functions or operations. Software code may be stored ina memory unit and be then executed by a processor. The memory unit maybe provided within or outside the processor to exchange data with theprocessor through the various means known to the public.

As mentioned in the foregoing description, the detailed descriptions forthe preferred embodiments of the present invention are provided to beimplemented by those skilled in the art. While the present invention hasbeen described and illustrated herein with reference to the preferredembodiments thereof, it will be apparent to those skilled in the artthat various modifications and variations can be made therein withoutdeparting from the spirit and scope of the invention. Therefore, thepresent invention is non-limited by the embodiments disclosed herein butintends to give a broadest scope matching the principles and newfeatures disclosed herein. In addition, although the present inventionhas been described with reference to the preferred embodiments thereof,it will be apparent to those skilled in the art that not only theinvention is not limited to the aforementioned specific embodiments butvarious modifications can be made in the present invention withoutdeparting from the spirit or scope of the invention. Such modificationsare not to be construed individually from the technical spirit and scopeof the present invention.

In addition, both an apparatus invention and a method invention areexplained in the present specification, and if necessary, theexplanation on both the inventions can be complementally applied.

INDUSTRIAL APPLICABILITY

The above-described method can be applied to not only the 3GPP systembut also various wireless communication systems including an IEEE802.16x system and an IEEE 802.11x system. Further, the proposed methodcan also be applied to an mmWave communication system using ultra highfrequency band.

What is claimed is:
 1. A method for performing, by a user equipment (UE)in a wireless communication system, the method comprising: receiving aphase tracking reference signal (PTRS) from a base station (BS); andperforming phase tracking operation based on the PTRS, wherein a PTRSpower boosting level of the PTRS is determined based on a number ofPhysical Downlink Shared Channel (PDSCH) layers associated with thePTRS.
 2. The method of claim 1, further comprising: receiving PTRS powerboosting information indicating a power boosting on/off state of thePTRS.
 3. The method of claim 2, wherein the PTRS power boostinginformation is received via radio resource control (RRC) signaling. 4.The method of claim 1, wherein when the number of PDSCH layers is L, thePTRS power boosting level satisfies 10*log₂(L).
 5. The method of claim1, wherein the number of PDSCH layers corresponds to a number ofDemodulation Reference Signal (DMRS) ports associated with the PTRS. 6.The method of claim 1, wherein the PTRS power boosting level is relatedto an energy per resource element (EPRE) ratio between the PTRS and acorresponding PDSCH.
 7. A user equipment (UE), the UE comprising: areceiver; a transmitter; and a processor configured to control thereceiver and the transmitter, wherein the processor is configured to:receive, through the receiver, a phase tracking reference signal (PTRS)from a base station (BS); and perform phase tracking operation based onthe PTRS, wherein a PTRS power boosting level of the PTRS is determinedbased on a number of Physical Downlink Shared Channel (PDSCH) layersassociated with the PTRS.
 8. The UE of claim 7, wherein the processor isfurther configured to receive, through the receiver, PTRS power boostinginformation indicating a power boosting on/off state of the PTRS.
 9. TheUE of claim 8, wherein the PTRS power boosting information is receivedvia through radio resource control (RRC) signaling.
 10. The UE of claim7, wherein when the number of PDSCH layers is L, the PTRS power boostinglevel satisfies 10*log₂(L).
 11. The UE of claim 7, wherein the number ofPDSCH layers corresponds to a number of Demodulation Reference Signal(DMRS) ports associated with the PTRS.
 12. The UE of claim 7, whereinthe PTRS power boosting level is related to an energy per resourceelement (EPRE) ratio between the PTRS and a corresponding PDSCH.
 13. Anon-transitory processor readable medium recorded thereon a program codefor executing the method of claim 1.